@incollection{JozefikKersteinSchmidt, author = {Jozefik, Zoltan and Kerstein, Alan R. and Schmidt, Heiko}, title = {Towards a compressible reactive multiscale approach based on One-Dimensional Turbulence}, series = {Active Flow and Combustion Control 2014}, booktitle = {Active Flow and Combustion Control 2014}, editor = {King, Rudibert}, publisher = {Springer}, address = {Switzerland}, isbn = {978-3-319-11967-0}, pages = {197 -- 211}, abstract = {Due to its huge complexity, progress in understanding and prediction of turbulent combustion is extremely challenging. In principle, progress is possible without improved understanding through direct numerical solution (DNS) of the exact governing equations, but the wide range of spatial and temporal scales often renders it unaffordable, so coarse-grained 3D numerical simulations with subgrid parameterization of the unresolved scales are often used. This is especially problematic for multi-physics regimes such as reacting flows because much of the complexity is thus relegated to the unresolved small scales. One-Dimensional Turbulence (ODT) is an alternative stochastic model for turbulent flow simulation. It operates on a 1D spatial domain via time advancing individual flow realizations rather than ensemble-averaged quantities. The lack of spatial and temporal filtering on this 1D domain enables a physically sound multiscale treatment which is especially useful for combustion applications where, e.g., sharp interfaces or small chemical time scales have to be resolved. Lignell et al. recently introduced an efficient ODT implementation using an adaptive mesh. As all existing ODT versions it operates in the incompressible regime and thus cannot handle compressibility effects and their interactions with turbulence and chemistry which complicate the physical picture even further. In this paper we make a first step toward an extension of the ODT methodology towards an efficient compressible implementation. The necessary algorithmic changes are highlighted and preliminary results for a standard non-reactive shock tube problem as well as for a turbulent reactive case illustrate the potential of the extended approach.}, language = {en} } @inproceedings{StollbergNamangoSchmidtetal., author = {Stollberg, Christian and Namango, Saul and Schmidt, M. and Pohl, R. and Ay, Peter}, title = {Preparation of plastics for automatic identification as the first step in recycling of automotive parts}, series = {Proceedings of the XXII International Mineral Processing Congress, Cape Town, South Africa, 29 September - 3 October 2003}, booktitle = {Proceedings of the XXII International Mineral Processing Congress, Cape Town, South Africa, 29 September - 3 October 2003}, publisher = {South African Institute of Mining \& Meta}, address = {Marshalltown, South Africa}, language = {en} } @misc{JahnBlaudeckBaumannetal., author = {Jahn, Stephan F. and Blaudeck, Thomas and Baumann, Reinhard R. and Jakob, Alexander and Ecorchard, Petra and R{\"u}ffer, Tobias and Lang, Heinrich and Schmidt, Peer}, title = {Inkjet Printing of Conductive Silver Patterns by Using the First Aqueous Particle-Free MOD Ink without Additional Stabilizing Ligands}, series = {Chemistry of Materials}, volume = {22}, journal = {Chemistry of Materials}, number = {10}, issn = {1520-5002}, doi = {10.1021/cm9036428}, pages = {3067 -- 3071}, abstract = {The chemical and physical properties of [AgO2C(CH2OCH2)3H] (3) and its use as an aqueous, ligand-free MOD ink (MOD = metal-organic decomposition) for piezo inkjet printing is discussed. The printed, thermal, or photochemical sintered silver features are electrically conductive on glass (2.7 × 107 S m-1) and PET (PET = polyethylene terephthalate) substrates (1.1 × 107 S m-1) corresponding to 43\% and 18\% of the bulk silver conductivity. Conducted tape tests show the suitability of the ink for particularly polymer substrates. TG-MS studies demonstrate a two-step decomposition for the conversion of 3 to elemental silver. The structure of 3 in the solid state was determined by single X-ray structure determination.}, language = {en} } @misc{JahnJakobBlaudecketal., author = {Jahn, Stephan F. and Jakob, Alexander and Blaudeck, Thomas and Schmidt, Peer and Lang, Heinrich and Baumann, Reinhard R.}, title = {Inkjet printing of conductive patterns with an aqueous solution of [AgO2C(CH2OCH2)3H] without any additional stabilizing ligands}, series = {Thin Solid Films}, volume = {518}, journal = {Thin Solid Films}, number = {12}, issn = {0040-6090}, doi = {10.1016/j.tsf.2010.01.030}, pages = {3218 -- 3222}, abstract = {The use of silver(I)-2-[2-(2-methoxyethoxy)ethoxy]acetate, [AgO2C(CH2OCH2)3H], and its application as an aqueous metal-organic decomposition (MOD) inkjet ink is reported. The chemical and physical properties of the silver carboxylate and the ink formulated thereof are discussed. The ink meets all requirements of piezo driven inkjet printing. The printed features were converted into electrically conducting silver patterns by thermal or photo-thermal treatment. The conversion of [AgO2C(CH2OCH2)3H] to elemental silver follows a two-step decomposition as demonstrated by thermogravimetry-mass spectrometry (TG-MS) measurements. The measured conductivities of the printed features on glass and polyethylene-terephthalate (PET) are 2.7 × 107 S m-1 and 1.1 × 107 S m-1, respectively, which correspond to 43\% (glass) and 18\% (PET) of the bulk silver conductivity.}, language = {en} } @misc{JozefikKersteinSchmidtetal., author = {Jozefik, Zoltan and Kerstein, Alan R. and Schmidt, Heiko and Lyra, Sgouria and Kolla, Hemanth and Chen, Jackie H.}, title = {One-dimensional turbulence modeling of a turbulent counterflow flame with comparison to DNS}, series = {Combustion and Flame}, volume = {162}, journal = {Combustion and Flame}, number = {8}, issn = {0010-2180}, doi = {10.1016/j.combustflame.2015.05.010}, pages = {2999 -- 3015}, abstract = {The one-dimensional turbulence (ODT) model is applied to a reactant-to-product counterflow configuration and results are compared with DNS data. The model employed herein solves conservation equations for momentum, energy, and species on a one dimensional (1D) domain corresponding to the line spanning the domain between nozzle orifice centers. The effects of turbulent mixing are modeled via a stochastic process, while the Kolmogorov and reactive length and time scales are explicitly resolved and a detailed chemical kinetic mechanism is used. Comparisons between model and DNS results for spatial mean and root-mean-square (RMS) velocity, temperature, and major and minor species profiles are shown. The ODT approach shows qualitatively and quantitatively reasonable agreement with the DNS data. Scatter plots and statistics conditioned on temperature are also compared for heat release rate and all species. ODT is able to capture the range of results depicted by DNS. However, conditional statistics show signs of underignition.}, language = {en} } @misc{JozefikKersteinSchmidt, author = {Jozefik, Zoltan and Kerstein, Alan R. and Schmidt, Heiko}, title = {Simulation of shock-turbulence interaction in non-reactive flow and in turbulent deflagration and detonation regimes using one-dimensional turbulence}, series = {Combustion and Flame}, volume = {164}, journal = {Combustion and Flame}, issn = {0010-2180}, doi = {10.1016/j.combustflame.2015.10.035}, pages = {53 -- 67}, abstract = {The one-dimensional turbulence (ODT) methodology is extended to include an efficient compressible implementation and a model for capturing shock-induced turbulence is presented. Lignell et al. recently introduced a Lagrangian ODT implementation using an adaptive mesh. As the code operates in the incompressible regime (apart from constant-pressure dilatation) it cannot handle compressibility effects and their interactions with turbulence and chemistry. The necessary algorithmic changes to include compressibility effects are highlighted and our model for capturing shock- turbulence interaction is presented. To validate our compressible solver, we compare results for the Sod shock tube problem against a finite volume Riemannsolver. To validate our model for shock-turbulence interaction, we present comparisons for a non-reactive and a reactive case. First, results of a shock traveling from light (air) to heavy (SF6) with recheck have been simulated to match mixing width growth data of experiments and turbulent kinetic energy results from LES.Then, for one-step chemistry calibrated to represent an acetylene/airmixture we simulate the interaction of a shock wave with an expanding flame front, and compare results with 2D simulation (2D-sim) data for flame brush formation and ensuing deflagration-to-detonation transitions (DDT). Results for the Sod shock tube comparison show that the shock speed and profile are captured accurately. Results for the non-reactive shock-recheck problem show that interface growth at all simulated Mach numbers is captured accurately and that the turbulent kinetic energy agrees in order of magnitude with LES data. The reactive shock tube results show that the flame brush thickness compares well to 2D-sim data and that the approximate location and timing of the DDT can be captured. The known sensitivity of DDT characteristics to details of individual flow realizations, seen also in ODT, implies that model agreement can be quantified only by comparing flow ensembles, which are presently unavailable other than in an ODT run-to-run sensitivity study that is reported herein.}, language = {en} } @misc{GlaweSchmidtKersteinetal., author = {Glawe, Christoph and Schmidt, Heiko and Kerstein, Alan R. and Klein, Rupert}, title = {XLES Part I: Introduction to Extended Large Eddy Simulation}, series = {arXiv.org}, journal = {arXiv.org}, pages = {38}, abstract = {Direct numerical simulation (DNS), mostly used in fundamental turbulence research, is limited to low turbulent intensities due the current and future computer resources. Standard turbulence models, like RaNS (Reynolds averaged Navier-Stokes) and LES (Large Eddy Simulation), are applied to flows in engineering, but they miss small scale effects, which are frequently of importance, see e.g. the whole area of reactive flows, flows with apparent Prandtl or Schmidt number effects, or even wall bounded flows. A recent alternative to these standard approaches is the one-dimensional turbulence (ODT) model, which is limited to 1D sub-domains. In two papers we will provide a generalized filter strategy, called XLES (extended LES), including a formal theory (part I) and one special approach in the XLES family of models, called ODTLES (in part II (see Glawe et al. (2015))). ODTLES uses an ODT sub-grid model to describe all turbulent scales not represented by XLES, which leaves the larger scales to be simulated in 3D. This allows a turbulence modeling approach with a 3D resolution mainly independent of the turbulent intensity. Thus ODTLES is able to compute highly turbulent flows in domains of moderate complexity affordably and including the full range of turbulent and diffusive scales. The convergence of XLES to DNS is shown and the unconventional XLES advection approach is investigated in basic numerical tests. In part II, highly turbulent channel and duct flow results are discussed and show the future potential of XLES and ODTLES.}, language = {en} } @misc{ChunSchmidtKucketal., author = {Chun, K. R. Julian and Schmidt, Boris and Kuck, Karl-Heinz and Andresen, Dietrich and Willems, Stefan and Spitzer, Stefan G. and Hoffmann, Ellen and Schumacher, Burghard and Eckardt, Lars and Seidl, Karlheinz and J{\"u}nger, Claus and Horack, Martin and Brachmann, Johannes and Senges, Jochen}, title = {Catheter ablation of atrial fibrillation in the young}, series = {Clinical Research in Cardiology}, volume = {102}, journal = {Clinical Research in Cardiology}, number = {6}, issn = {1861-0684}, doi = {10.1007/s00392-013-0553-6}, pages = {459 -- 468}, language = {en} } @misc{EfimovaVargaMatuscheketal., author = {Efimova, Anastasia and Varga, Janos and Matuschek, Georg and Saraji-Bozorgzad, Mohammad R. and Denner, Thomas and Zimmermann, Ralf and Schmidt, Peer}, title = {Thermal Resilience of Imidazolium-Based Ionic Liquids—Studies on Short- and Long-Term Thermal Stability and Decomposition Mechanism of 1-Alkyl-3-methylimidazolium Halides by Thermal Analysis and Single-Photon Ionization Time-of-Flight Mass Spectrometry}, series = {Journal of Physical Chemistry B}, volume = {122}, journal = {Journal of Physical Chemistry B}, number = {37}, doi = {10.1021/acs.jpcb.8b06416}, pages = {8738 -- 8749}, abstract = {Ionic liquids are often considered as green alternatives of volatile organic solvents. The thermal behavior of the ionic liquids is relevant for a number of emerging large-scale applications at elevated temperature. Knowledge about the degradation products is indispensable for treatment and recycling of the used ionic liquids. The objective of this paper was an investigation of the short- and long-term stability of several 1-alkyl-3-methylimidazolium halides, determination of the degradation products, and the elucidation of their decomposition patterns and structure-stability relations. Short-term stability and mechanism of thermal degradation were investigated by a self-developed, innovative thermal analysis single-photon ionization time-of-flight mass spectrometry device with Skimmer coupling. The applied technology provides real-time monitoring of the forming species and allows tracing their change during the course of the decomposition. Therein, the almost fragment-free soft ionization with vacuum ultraviolet photons plays a crucial role. We have detected unfragmented molecules whose formation was only assumed by electron ionization. Nevertheless, the main decomposition products of the selected ionic liquids were alkyl imidazoles, alkenes, alkyl halides, and hydrogen halides. From the decomposition products, we have deduced the fragmentation patterns and discussed their interrelation with the length of the alkyl chain and the type of the halide anion. Our results did not suggest the evaporation of the investigated ionic liquids prior to their decomposition under atmospheric conditions. Long-term thermal stability and applicability were determined based on thermogravimetric analysis evaluated with a kinetic model. Thus, the time-dependent maximum operation temperature (MOT) for the respective ionic liquids has been calculated. As a rule, the short-term stability overestimates the long-term decomposition temperatures; the calculated MOT are significantly lower (at least 100 K) than the standardly obtained decomposition temperatures.}, language = {en} } @misc{KleinKersteinSchmidt, author = {Klein, Marten and Kerstein, Alan R. and Schmidt, Heiko}, title = {Stochastic modeling of transient boundary layers in high-Rayleigh-number thermal convection}, series = {25th International Congress of Theoretical and Applied Mechanics (ICTAM 20+1)}, journal = {25th International Congress of Theoretical and Applied Mechanics (ICTAM 20+1)}, pages = {2}, abstract = {One-dimensional turbulence (ODT) modeling is used to investigate the boundary layer in high-Rayleigh-number thermal convection for a notionally infinite horizontal layer of fluid. The model formulation distinguishes between turbulent advection, which is modeled by a stochastic process, and deterministic molecular diffusion to capture relevant vertical transport processes (including counter-gradient fluxes). For this study, statistical homogenization is applied to the two horizontal dimensions so that we use ODT as stand-alone tool. We show that the model yields mean and fluctuation temperature profiles that are in several respects consistent with available reference data. Furthermore, the profile of a surrogate for the fluctuation velocity is reminiscent of canonical wall turbulence.}, language = {en} }